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Show 1894.] SALMONOID FISHES O E T H E E N G L I S H C H A L K . 657 British Museum exhibit both the head and trunk with fins, aud these form the basis of the following detailed description. The hinder half of the cranial roof, the facial and opercular bones, and the upper branchiostegal rays are ornamented with rugae, mostly radiating. The cranial roof is flattened, with a faint tendency to a depression mesially, aud the occipital border is excavated by a re-entering angle. The parietal bones (Plate XLII. fig. 2, pa.) are relatively small, longer than broad, and meet throughout their length in the median line, excluding the supra-occipital from the roof. The squamosals (fig. 2, sq.) flank the parietals, forming the postero-external angle of the cranial roof, and produced forwards a little along the outer margin of the frontals. The frontals (figs. 2, 3 a,fr.) are very large, broad, and rugose behind, tapering and nearly smooth forwards. In their hinder half the median suture between them is feebly dentated; the anterior extremity of each exhibits a A-shaped excavation (fig. 3 a). Occupying an indent in the outer margin of each frontal above and partly in advance of the orbit is a rugose elongated membrane-bone covering the prefrontal region, which is perhaps best named supraorbital (fig. 2, sp.o.). The depressed and expanded ethmoidal region (fig. 3 a, eth.) is widest at the palatine articulation. The supraoccipital exhibits a large vertical keel on its hinder face, but neither the occipital nor otic elements are sufficiently well displayed for description. In the pterygopalatine arcade the quadrate (figs. 3, 4, qu.) is often seen. It is triangular in shape, with a robust articular head, and an upwardly directed process arising from the lower end of its hinder border, clasping the thick styliform symplectic (fig. 4, sym.). The whole of its upper margin is apposed to the thin triangular metapterygoid (figs. 3, 4, m.pt.), and its anterior edge is similarly in contact Avith the downwardly curved hinder extremity of the ectopterygoid (fig. 3, ectp.). The twisted and expanded hyomandibular is also shown in one specimen, reaching the upper end of the symplectic; and there are remains of a relatively large and thin, antero-posteriorly elongated entopterygoid. In specimen no. P. 5680 there is evidence of minute clustered, pointed teeth on some thin internal bone; and this m a y have been either ecto- or ento-pterygoid. The maxilla (figs. 3, 5, mx.) is robust and arched, Avith a large upwardly directed process at its anterior end and a comrex oral margin. The upper portion is overlapped by two large supramaxillaries (figs. 3, 5, s.mx. i, 2), the hinder the deepest, and sending a narrow process forwards above the upper margin of the anterior plate. The premaxilla, underlapping the maxilla, is small, and both this and the maxilla are provided with very minute clustered teeth. The dentary portion of the mandible (figs. 5 a, 6, d.) is very robust at the symphysis, with a cluster of minute teeth in several series ; the points of attachment of these teeth are shown in fig. 5 a. The dentary rises in the coronoid region, and its hinder margin is excavated for the reception of the large angular (fig. 6, ag.). The lower border of the mandible is slightly bent inwards; and just PROC. ZOOL. Soc-1894, No. XLIV. 44 |